Still, even with what you say, they could consume/swallow/destroy our planet.
Not really. Here's the thing...
A black hole's size is determined by its mass. In the case of the collider, the mass is determined by how much energy is in the particles that collide. In terms of mass, that energy is very small.
Let us assume, for the moment, that the LHC does create a stable black hole. That hole would have very small mass, and thus very, very small size. A size on the order of a sub-atomic particle, if I recall the calculations correctly. It is tiny.
Black holes that come from stars "suck in" other matter in space not because they are black holes, but because they typically have have the mass of one or more (or many more) stars. This little guy has the mass of a few atoms. Not much gravity, so it doesn't suck.
Thus, the only way it eats up the matter of the planet is if it collides with it. But colliding with it is unlikely, because it is so very, very small. It will basically pass through normal matter without really noticing. It may collide with something, on occasion, as it floats around in an orbit around the planet's core.
In theory, such a thing might eat the planet, eventually. However, if collisions with normal atoms are so infrequent that it takes longer to do that than it takes our Sun to burn out, it really isn't much of an issue for us.
Plus, if it does accidentally create them, we then have to hope they are right that the holes will be tiny and only last moments. If they are wrong, which is totally possible because we know very little about Black Holes, and they could self stabilize as soon as created due to their very own nature, that is the risk "fanatics" are afraid of.
They will only be tiny. Even the theory that the fanatics point to says that. There is not enough energy in the beam to make a big hole. You don't create mass (energy) out of nothing.
No scientist can say with absolute certainty that if the collider does create a black hole that it is not capable of stabilizing and staying in existence.
Yes, and no scientist can say "with absolute certainty" that you won't collapse into a pile of your constituent atoms after the next time you watch
The Simpsons. That doesn't mean you actually treat that as a likely event.